Effect of blocking angiotensin II receptor subtype on rat sympathetic nerve function

Area of Science:

• Cardiovascular Pharmacology
• Neuropharmacology
• Renal Physiology

Background:

• Sympathetic nervous system activity and Angiotensin II (Ang II) interact to regulate cardiovascular function.
• Ang II receptors, specifically AT1 and AT2 subtypes, mediate distinct physiological effects.
• Understanding the role of Ang II in sympathetic neurotransmission is crucial for cardiovascular drug development.

Purpose of the Study:

• To investigate the role of Ang II receptor subtypes in modulating sympathetic function in pithed rats.
• To determine the specific Ang II receptor subtype involved in the interaction between Ang II and sympathetic norepinephrine release.
• To elucidate the contribution of Ang II to norepinephrine-mediated hemodynamic changes.

Main Methods:

• Hemodynamic parameters including mean arterial pressure, cardiac output, total peripheral resistance, and heart rate were measured in pithed rats.
• Effects of spinal cord stimulation and exogenous norepinephrine were assessed.
• Selective Ang II receptor subtype antagonists, losartan (AT1-selective) and PD123177 (AT2-selective), were administered to evaluate their impact on hemodynamic responses.

Main Results:

• Losartan (AT1 antagonist) blocked Ang II-induced hemodynamic responses and inhibited responses to spinal cord stimulation and norepinephrine, particularly affecting mean arterial pressure and total peripheral resistance.
• PD123177 (AT2 antagonist) did not alter hemodynamic responses to Ang II, spinal cord stimulation, or norepinephrine.
• These findings indicate that endogenous Ang II facilitates norepinephrine release from sympathetic nerve terminals.

Conclusions:

• The prejunctional Ang II receptor involved in facilitating norepinephrine release in pithed rats is primarily of the subtype 1 (AT1).
• This AT1 receptor plays a significant role in mediating the interaction between Ang II and sympathetic vascular tone.
• The results highlight the importance of the AT1 receptor in sympathetic neurotransmission and suggest potential therapeutic targets for cardiovascular diseases.